1. Field of the Invention
The present invention relates to a sandwich panel which is effectively usable as a material for interior walls, exterior walls, roofs, ceilings, floors, partitions, fireproofing doors, etc. of buildings, and which does not suffer deformation such as swelling, warping or the like after it is manufactured and has excellent mechanical strength.
2. Description of Related Art
There have been hitherto proposed and put on the market various sandwich-type composite panels (hereinafter referred to as "sandwich panel") each of which basically has a sandwich structure that a core member formed of synthetic resin foam is integrally sandwiched between a front surface member and a back surface member. However, these sandwich panels, particularly sandwich panels whose core members are manufactured by an injection molding method of injecting liquid or particle material, have the following problem. That is, when the core member is formed of synthetic resin foam such as phenol foam, polyurethane foam, polyisocyanurate foam or the like, the surface of a sandwich panel suffers deformation such as swelling, warping or the like with time lapse due to internal gas such as unreacted components of those components which are used to form the core member, surplus undesired gas components which are produced through a chemical reaction for forming the core member (for example, chlorine gas, carbon dioxide, methylene chloride, formaldehyde, steam, or hydrogen) or the like, so that the external appearance of a facing is greatly damaged due to the deformation (swelling, warping or the like).
Particularly in a case where phenol resin raw liquid, acidic hardening agent and forming agent are mixed with each other and injected to form phenol foam raw material (resol type) for the core member through a foaming reaction, the condensation water of 10 wt % is produced through the reaction and trapped in the phenol foam. The trapped water is steamed in a produced panel due to variation of an outside temperature or the like during a foster period of the sandwich panel or after a panel securing work is executed, and remains as gas in the core member, in a gap between the core member and each of the front and back surface members of the sandwich panel because there is no leak path through which the internal gas thus produced is discharged to the outside of the panel. Therefore, the gas swelling is liable to occur between the core member and each of the front and back surface members of the sandwich panel, the front surface member and/or back surface member is liable to warp, and/or the mechanical strength of the panel is lowered, so that the external appearance of the sandwich panel and the mechanical strength thereof are varied with time lapse.
Furthermore, in the sandwich panel thus constructed, the front surface member and the back surface member are drawn toward a heating side due to the difference in thermal conductivity therebetween and thus they are greatly deformed in different directions. This deformation causes a gap at a link portion between sandwich panels, and heat and flame leaks to the opposite side through the gap. Therefore, these panels cannot pass a fireproofing construction one-hour test of JIS-A-1304.
Still furthermore, a sandwich panel which is obtained by merely sandwiching a phenol foam body serving as the core member between the front surface member and the back surface member is weak in mechanical strength because its core member is formed of synthetic resin foam, and thus it is weak in bending strength and resistance against wind pressure. In addition, a securing pitch of sandwich panels in a securing work becomes short, and thus its workability is low. Furthermore, the adhesive strength between the core member and each of the front and back surface members is weak, and thus the core member and each of the front and back surface members are liable to be peeled off from each other particularly at the end portions thereof due to a slight impact. The undesired (surplus) gas, etc. as described above are liable to occur particularly in a high-temperature midsummer (a season when the front surface member is humidified).